If you ask Fantastic Fan for "Trouble Shoot #9A - Customer Wants To Slow the Fan" doc, it shows them simply adding more resistors.
When you replace the 3 speed switch with the rheostat you eliminate all the original resistors. With the 50 ohm rheostat I can seamlessly slow it to a crawl at minimum setting but it does not stop. I used a touch of dielectric grease between the wiper and the windings which maybe helps. It does not tick or make any noises dialing in any slow settings. Only extra cost was the orig 3 speed knob did not fit my rheostat shaft. I got $2 one from Radio Shack that did.